1. Field of the Invention
The present invention relates generally to a fluid-filled type vibration-damping device designed to produce vibration damping effect on the basis of flow action of a non-compressible fluid sealed within its interior; and more particularly to a fluid-filled type vibration-damping device having a flexible plate as a fluid pressure absorbing mechanism.
2. Description of the Related Art
Rubber vibration dampers comprising a first mounting member and a second mounting member connected by a main rubber elastic body are widely employed in a variety of fields as vibration-damped connectors or vibration-damped supports installed between components that make up a vibration transmission system. As one type of rubber vibration damper of this kind, there have been proposed fluid-filled type vibration-damping devices that utilize resonance or other flow action of a non-compressible fluid sealed within the device. As one such vibration-damping device, there is known a fluid-filled type vibration-damping device that typically comprises: a first mounting member and a second mounting member attached respectively to a vibration-damped member and a vibrating member and connected together by a main rubber elastic body; a pressure-receiving chamber whose wall is partially constituted by the main rubber elastic body and that gives rise to pressure fluctuations when vibration is input; an equilibrium chamber whose wall is partially constituted by a flexible film and which allows change in volume; a non-compressible fluid sealed within the pressure-receiving chamber and the equilibrium chamber; and an orifice passage interconnecting the two chambers.
Vibration damping effect based on resonance of the non-compressible fluid induced to flow through the orifice passage is achieved only in the specific frequency range to which the device has been pre-tuned. Accordingly, in order to improve vibration damping ability, while avoiding markedly high dynamic spring constant exhibited particularly when vibration of a higher frequency range than the tuning frequency of the orifice passage is input, there has been proposed a fluid pressure absorbing mechanism, which employs a movable plate. The fluid pressure absorbing mechanism is typically constructed by forming a housing space in the partition member that divides the pressure-receiving chamber and the equilibrium chamber, and disposing a movable plate housed within this housing space so as to permit minute displacement thereof. The housing space connects with the pressure-receiving chamber and the equilibrium chamber via through-holes, and pressure in the pressure-receiving chamber is exerted on one face of the movable plate, while pressure in the equilibrium chamber is exerted on the other face.
Displacement of the movable plate based on a pressure differential between the pressure-receiving chamber and the equilibrium chamber enables minute pressure fluctuations produced in the pressure-receiving chamber during input of vibration in the high-frequency range to escape into and be absorbed in the equilibrium chamber. During input of vibration of the low-frequency range to which the orifice passage has been tuned, on the other hand, due to the large amplitude of the vibration, the movable plate is forced into contact against the inside face of the housing space, and in a state of being juxtaposed or superimposed against it substantially blocks off the through-hole. Consequently, absorption of pressure of the pressure-receiving chamber by the fluid pressure absorbing mechanism is avoided, so that the relative pressure fluctuations are produced effectively in the pressure-receiving chamber and the equilibrium chamber, ample fluid flow through the orifice passage between the two chambers is assured, and vibration damping action is produced by the orifice passage.
In this kind of fluid pressure absorbing mechanism, when sharp pressure fluctuations are produced in the pressure-receiving chamber by input of large-amplitude vibration, the movable plate is caused to strike forcefully against the inside wall of the housing space. A resultant problem is that the impact of the movable plate striking against the inside wall of the housing space tends to produce noise and vibration. For example, where employed as an automotive engine mount, noise that is audible to the driver can be produced during engine cranking or when driving over bumps, which poses the risk of contributing to diminished drive feel.
To address such problems, it has been proposed, for example in JP-Y2-4-33478, to fabricate the movable plate from a rubber elastic plate, and to integrally form a small projection of rib form on the surface thereof, whereby the impact of striking can be absorbed by this small projection. However, while such a small projection has been found effective against striking at relatively low energy, in the event of a sudden large pressure fluctuation in the pressure-receiving chamber, adequate effectiveness is not readily achieved, making further improvement desirable.